Process for making foams by photopolymerization of emulsions

ABSTRACT

The invention discloses methods for making foams by photopolymerizing emulsions comprising a reactive phase and a phase immiscible with the reactive phase components. Foams made from water-in-oil emulsions, including high internal phase emulsion are disclosed. Articles and uses for the foams are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 09/398,355, filed Sep.17, 1999 now U.S. Pat. No. 6,573,305, the disclosure of which is hereinincorporated by reference.

TECHNICAL FIELD

This invention relates to foams made by photopolymerizing emulsions. Theemulsions comprise a reactive phase and an immiscible phase wherein thereactive phase or both phases are continuous. The resulting foams may beclosed or open cell, depending on the initial emulsion microstructure.

BACKGROUND

In the past, thermal polymerization has been used as a technique topolymerize high internal phase emulsions (HIPE)s. Typically these HIPEscontain styrene and divinylbenzene as well as other monomers. Thethermal polymerization technique is very time intensive, usuallyrequiring more than 10 hours for polymerization, and prohibitscontinuous production of foams. For thermal polymerization, emulsionsare made and poured into a sealed container in which they are heated formany hours. After polymerization, the solid foams (still containingwater) are removed and dried in an oven.

The emulsions used in thermal polymerization must remain stable for manyhours until the polymerization process is complete, otherwiseinhomogeneous foam materials would be formed. The requirement for astable emulsion limits the types of monomers and surfactants that may beused in a thermal polymerization process.

SUMMARY OF INVENTION

The present invention features a novel method for creating foams,including open cell foams, from water-in-oil emulsions. The applicantsfound, surprisingly, that they could make foams from high internal phaseemulsions (HIPEs) and other water-in-oil emulsions using aphotopolymerization process. This is unexpected because emulsionstypically have an opaque appearance and would not be expected totransmit enough light to conduct a photopolymerization reaction.Applicants found that they could cure an emulsion as thick as 8millimeters.

The foams may be made by a batch process, or a continuous process inwhich the emulsion may be coated on a moving support. In either case,the foam is polymerized and crosslinked by exposure to actinicradiation. Some embodiments of the foams may be polymerized andcrosslinked within one second or less of radiation illumination time.The fast polymerization process of the present invention allows a broadrange of materials to be used because the emulsion needs to be stablefor only a short time (seconds to minutes).

One aspect of the present invention provides a process for making acrosslinked polymeric foam comprising: a) mixing a reactive phasecomprising at least one polymerizable material, at least onecrosslinking agent, and at least one emulsifier with at least onephotoinitiator and a liquid fluid immiscible with the reactive phase toform an emulsion wherein the immiscible fluid forms a discontinuous orco-continuous phase with the continuous reactive phase; b) shaping theemulsion; and c) exposing the emulsion to actinic radiation to form acrosslinked polymeric foam containing residual immiscible fluid.

The process may comprise further steps of exposing the emulsion to heatand/or removing residual immiscible fluid from the foam.

The polymerizable material may be ethylenically- oracetylenically-unsaturated, such as an acrylate, and free-radically orcationically-curable. The polymerizable material may be the same as thecrosslinking agent or the emulsifier.

The immiscible phase is typically water, but may comprise other liquidssuch as fluorocarbons or organic liquids. The immiscible fluid maycomprise 74 volume percent, or more, of the emulsion.

The reactive phase may include, e.g., non-polymerizable materials andmaterials that can incorporate functional groups into the foam.

The structure of the foam of the present invention may be controlled byaging the emulsion prior to polymerization or by selection of aparticular agitation method for making the emulsion.

The emulsion may include photoinitiators in the reactive or immisciblephase. Preferably, the photoinitiators are activated by ultraviolet orvisible radiation of 300 to 800 nanometers.

Polymerization and crosslinking of the emulsion may occur in as littleas 10 minutes or even 10 seconds.

A further aspect of the invention is an emulsion having a continuousreactive phase comprising at least one polymerizable material and atleast one crosslinking agent, a discontinuous or co-continuous phasecomprising a liquid fluid immiscible with the reactive phase, and atleast one photoinitiator.

A further aspect of the invention is an open cell cross-linked foamcomprising no thermal initiator residue. Another aspect of the inventionis an open cell cross-linked foam comprising residue of a photoinitiatorthat absorbs at a wavelength of 300 to 800 nanometers.

A further aspect of the invention is a closed cell cross-linked foamcomprising no thermal initiator residue. Another aspect of the inventionis a closed cell cross-linked foam comprising residue of aphotoinitiator that absorbs at a wavelength of 300 to 800 nanometers.

The foams may be crosslinked within the voids of a material selectedfrom the group consisting of polymeric, woven, nonwoven, and metals.Alternatively, the foam may contain non-polymerizable materials selectedfrom the group consisting of polymers, metals, particles, and fibers.

Some foams of the present invention can absorb at least two and one-halftimes their weight in fluid. Some of the foams collapse when fluid isremoved.

Another aspect of the present invention is articles made using the foamsof the present invention.

Foams of the present invention made from HIPEs have relativelyhomogeneous structures and may possess cell sizes between 1 and 200microns and densities of at least 0.01 g/cc. Cells are typically joinedby open “windows” or holes connecting adjacent cells. Some of theresulting foam materials may be capable of absorbing 25 or more times,typically 4 to 16 times, their weight in fluid (water or organicfluids). Some of the foams are extremely porous, having Gurley values(at 50 cc of air) of 2 to 70 seconds for a 0.2 cm (80 mil) thickspecimen.

Foams of the present invention made from non-HIPE emulsions typicallyhave interconnecting channel structures rather than a well-definedcellular structure.

Closed cell foams may also be made using the photopolymerization processof the present invention.

As used in this invention:

“HIPE” or “high internal phase emulsion” means an emulsion comprising acontinuous reactive phase, typically an oil phase, and a discontinuousor co-continuous phase immiscible with the oil phase, typically a waterphase, wherein the immiscible phase comprises at least 74 volume percentof the the emulsion;

“water-in-oil emulsion” means an emulsion containing a continuous oilphase and a discontinuous water phase; the oil and water phases may beco-continuous in some cases;

“reactive phase” means the continuous phase which contains the monomeror reactive species that are sensitive to reactive propagating species(e.g., those having free radical or cationic centers) and can bepolymerized or crosslinked;

“immiscible phase” means a phase in which the reactive components havelimited solubility; the immiscible phase may be discontinuous, orco-continuous with the reactive phase;

“stable” means the composition and microstructure of the emulsion is notchanging over time;

“functional group” means a chemical entity capable of undergoing anon-polymerization reaction;

“monomer” means chemical species capable of polymerizing, it includesmonomers and oligomers;

“reactive surfactant” means a surfactant (i.e., emulsifier) havingsufficient reactivity to undergo polymerization reactions such that itbecomes part of a polymer backbone;

“open cell” means a foam wherein the majority of adjoining cells are inopen communication with each other; an open cell foam includes foamsmade from co-continuous emulsions in which the cell structure is notclearly defined, but there are interconnected channels creating at leastone open pathway through the foam;

“window” means an intercellular opening;

“shaping” means forming into a shape and includes pouring, coating, anddispensing;

“polymerize” or “cure” are used interchangeably in this application andindicate a chemical reaction in which monomers, oligomers, or polymerscombine, including by crosslinking, to form a chain or network;

“crosslinking” means the formation of chemical links between polymerchains;

“crosslinking agent” means a material that adds to a polymer chain asite capable of forming a link to another polymer chain;

“cationically curable monomer” means a monomer capable of undergoingpolymerization in which cationic species propagate the polymerizationreaction and includes monomers containing, e.g., epoxide or vinyl ethermoieties;

“ethylenically unsaturated” means a monomer having a carbon—carbondouble bond in its molecular structure;

“acetylenically unsaturated” means a monomer having a carbon—carbontriple bond in its molecular structure;

“actinic radiation” means photochemically active radiation includingnear infrared radiation, visible light, and ultraviolet light;

“UV” or “ultraviolet” means actinic radiation having a spectral outputbetween about 200 and about 400 nanometers;

“visible light” means actinic radiation having a spectral output betweenabout 400 to about 800 nanometers;

“near infrared” means actinic radiation having a spectral output betweenabout 800 to about 1200 nanometers;

“photoinitiator” means a chemical added to selectively absorb actinicradiation and generate reactive centers such as free radicals andcationic species;

“thermal initiator” means a species only capable of efficiently inducingor causing polymerization or crosslinking by being exposed to heat;

“homogeneous composition” means having a uniform distribution ofchemical components when examined on a scale of 0.5 micrometers;

“pressure sensitive adhesive” or “PSA” means an adhesive that willadhere to a variety of dissimilar surfaces upon mere contact without theneed of more than finger or hand pressure; PSAs are sufficientlycohesive and elastic in nature so that, despite their aggressivetackiness, they can be handled with the fingers and removed from smoothsurfaces with little or no residue left behind; PSAs can bequantitatively described using the “Dahlquist criteria” which maintainsthat the elastic modulus of these materials is less than 10⁶ dynes/cm²at room temperature. See Pocius, A. V., Adhesion & Adhesives: AnIntroduction, Hanser Publishers, New York, N.Y., First Edition, 1997,and

“void” means any open space, in a foam, such as holes, cells, andinterstices.

An advantage of at least one embodiment of the present invention is thatthe photopolymerization process may be completed in seconds as opposedto thermal polymerization methods that typically require many hours.

An advantage of at least one embodiment of the present invention is thatthe faster polymerization process allows the use of emulsioncompositions that cannot remain stable for the length of time requiredto complete thermal polymerization.

An advantage of at least one embodiment of the present invention is thata broad spectrum of foam physical properties can be generated bymanipulating the type of monomers and co-monomers, the monomer toco-monomer ratio, cell size, percentage of open cells, density of thefoam, and mixing methods.

An advantage of at least one embodiment of the present invention is thatthe process allows continuous foam production as opposed to the batchprocessing generally required with thermal polymerization ofwater-in-oil emulsions.

An advantage of at least one embodiment of the present invention is thatsalts in the water phase of the emulsion are not necessary to providelengthy stability during emulsification and polymerization. This alsoeliminates the need to wash away excess salts after polymerization.

An advantage of at least one embodiment of the present invention is thatthin foam articles can be produced directly by the present method asopposed to having to cut thin articles from the products of a batchthermal polymerization process.

An advantage of at least one embodiment of the present invention is thatthe foams may be hydrophilic when produced, depending on monomer andsurfactant choice. This eliminates having to incorporate hydrophilizingagents or treat the foam surfaces to make them hydrophilic (e.g., whenused as an absorbent) as is required with some thermally polymerizedfoams.

An advantage of at least one embodiment of the present invention is thatfoams having a wide range of cell and window sizes can be obtainedbecause the method of the present invention allows foams to be made fromemulsions that are stable for as little as one minute or less.

An advantage of at least one embodiment of the present invention is thatthe foam materials are suitable for a myriad of applications such asenergy and fluid absorption, insulation, and filtration. An advantage ofat least one embodiment of the present invention is that multilayerarticles comprising one or more foam layers may be made.

An advantage of at least one embodiment of the present invention is thatarticles comprising regions, i.e., areas, having foams that differ incomposition or density may be made.

An advantage of at least one embodiment of the present invention is thatthe foams may be made by a continuous process.

Other features and advantages of the invention will be apparent from thefollowing drawings, detailed description, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows scanning electron microscope (SEM) digital imagemicrographs of a cross section of an open-cell foam of the presentinvention at magnifications of 100×, 300×, and 1,000×, respectively,from top to bottom.

FIGS. 2a and 2 b show SEM digital image micrographs of cross sections ofopen-cell foams of the present invention wherein the foam shown in 2 bwas agitated more than the foam shown in 2 a. The left-hand columns ofmicrographs in both 2 a and 2 b show the foams in an unhydrated(collapsed) state; the right-hand columns show the foams in a hydratedstate (SEMs were obtained by freeze-drying the samples). Magnificationsof the foam, from top to bottom, respectively, are 150×, 500×, 1,500×,and 5,000×.

FIGS. 3a-3 c show SEM digital image micrographs of cross sections ofopen-cell foams produced from the same emulsion but polymerized atdifferent intervals after the emulsion was made. For 3 a-3 c, thesetimes were immediate, 15 minutes, and 3 days, respectively.Magnifications of the foams, from top to bottom, respectively, are 100×,300×, and 1,000×.

FIG. 4 shows SEM digital image micrographs of cross sections ofopen-cell foams of the present invention having different foamdensities. The densities of the foams increase from right to left.Magnification of the foam increases from bottom to top, with themagnifications being 60×, 300×, and 1,000×, respectively.

FIG. 5 shows SEM digital image micrographs of cross sections ofopen-cell foams of the present invention made with different amounts ofemulsifier, sorbitan monooleate (SMO). Emulsifier concentrationincreases from right to left. Magnification of the foam increase frombottom to top, with the magnifications being 100×, 300×, and 1,000×,respectively.

FIG. 6 shows SEM digital image micrographs of a cross section of anopen-cell collapsible foam of the present invention in both anunhydrated (left column) and hydrated (right column) state. The foam waspolymerized using a Xenon flashlamp. Magnifications of the foam, fromtop to bottom, respectively, are 150×, 500×, 1,500×, and 5,000×.

FIG. 7 shows SEM digital image micrographs of a cross section of anopen-cell foam of the present invention made by a process comprisingcontinuous emulsion-making. Magnifications of the foam, from top tobottom, respectively, are 100×, 500×, and 1,000×.

FIG. 8 shows SEM digital image micrographs of a cross section of a foamof the present invention having an interconnecting channel structure.Magnifications of the foam, from top to bottom, respectively, are 100×,500×, and 1,000×.

FIG. 9 shows SEM digital image micrographs of a cross section of a foamof the present invention made with a rotor-stator mixer. Magnificationsof the foam, from top to bottom, respectively, are 100×, 300×, and1,000×.

FIG. 10 shows SEM digital image micrographs of a cross section of a foamof the present invention made with a pin mixer. Magnifications of thefoam, from top to bottom, respectively, are 100×, 500×, and 1,000×.

DETAILED DESCRIPTION

Polymeric foams of the present invention may be made byphotopolymerizing HIPES (emulsions having relatively highreactive-to-immiscible phase volume/ratios of approximately 3:1 to 15:1or greater). Although water is typically used as the immiscible phase,any fluid that is a liquid at operating conditions and is substantiallyimmiscible with the oil (reactive) phase components could be used.Having a non-aqueous immiscible phase allows the use of water-soluble(not merely hydrophilic), as well as ethylenically unsaturated, oracetylenically unsaturated reactants in the reactive phase. (In thepresent invention, acetylenically unsaturated reactants may be used inany case where ethylenically unsaturated reactants may be used.)Additionally, a nonaqueous immiscible phase can enable water-sensitivepolymerization methods, such as cationic polymerization.

For cationic polymerizations, it is often useful to illuminate theemulsion with UV or visible light (starting the photopolymerization byactivating a catalyst) and follow this activation step with someheating. The propagating species in cationic polymerizations are muchlonger-lived than those in free radical polymerizations, and cancontinue to propagate without illumination (i.e., during the heatingstep). The reactive species in free radical polymerizations aretypically much shorter lived and do not continue to propagate once thelight source is removed. The benefit of conducting a post heating stepon foams made from cationically polymerizing materials is that thereactivity of the materials (e.g. epoxies) is supplemented by heating.Additionally, greater temperature will provide greater diffusion in apolymerizing system, leading to increased levels of monomer conversion.Enhancements in physical properties are usually produced by post-heatingcationically polymerizing systems that were first activated throughphotopolymerization. These effects can also be produced by maintainingelevated temperatures during the photopolymerization process, but notconducting a separate post-heating step at the end. In fact, freeradical polymerizations can also be driven to higher levels ofconversion if they are maintained at elevated temperatures during thephotopolymerization step. In the current invention, however, some of theemulsion compositions (containing free radically polymerizablematerials) are unstable at elevated temperatures, and in these cases itis undesirable to deliberately increase the temperature of the emulsionsystem before or during the photopolymerization.

Emulsions having co-continuous reactive and immiscible phases, may alsobe used to make foams of the present invention, e.g., a water-in-oilemulsion with a water to oil ratio of less than 3:1.

The emulsions of the present invention contain a photoinitiatingspecie(s). The photoinitiating specie(s) may be present in either phase.The emulsions do not require a thermal initiating species. Thermalinitiators include, e.g., azo compounds, peroxides, peroxy carbonates,peroxycarboxylates, potassium persulfate, t-butyl peroxyisobutyrate, and2,2′-azobisisobutyronitrile.

After the emulsions are formed, they may be polymerized and crosslinkedby exposure to actinic radiation, e.g., ultraviolet and visibleradiation. Removal of the immiscible phase will typically leave an opencell foam structure. Closed cell foams may also be made according to thepresent invention.

The relative amounts of immiscible and reactive phase components used toform the emulsions of the present invention, among many otherparameters, is important in determining the structural, mechanical, andperformance properties of the resulting polymeric foams. The immiscibleto reactive phase volume ratio can influence foam characteristics suchas density, cell size, cell structure, and dimensions of struts thatform the foam structure. The density and microstructure of the foam alsodepend on aspects of the emulsion-making process (rate of immisciblephase addition to the reactive phase, agitation method, etc.).

The emulsions of the present invention can be photopolymerized rapidly.They may be polymerized in less than one hour, preferably less than 10minutes, more preferably less than 30 seconds, still more preferablyless than 10 seconds, and most preferably less than 1 second. This rapidpolymerization allows a wider variety of compositions to be used,compared to those suitable for thermal polymerization techniques. Thisis partly due to emulsion stability requirements. Becausephotopolymerization can occur quickly with the method of the presentinvention, the emulsion need only be stable for a short period of time,e.g., up to several minutes, as compared to hours of stability requiredfor thermal polymerization.

The emulsions may also be applied onto or into materials beforepolymerization so that the reactive phase of the emulsion polymerizes inand around the material, thus incorporating the material into the foamstructure. The incorporated materials can provide the foam with strengthand other desirable properties. Suitable materials include porous oropen-weave materials such as woven, nonwoven, fibrous, and particulatematerials, including scrims. The foams may also be coated, andpolymerized, on nonporous materials such as paper, polymer, metalmaterials, and microstructured substrates.

Light in the visible and/or ultra-violet range (200 to about 800 nm) ispreferably used to polymerize the emulsions of the present invention.Due to the high tendency of emulsions to scatter light, it is preferableto use long wavelengths in this range because they are better able topenetrate the emulsions. Preferable wavelengths are 200 to 800nanometers, more preferably 300 to 800 nanometers, most preferably 300to 450 nanometers because of the availability of photoinitiatorsactivated at these wavelengths and availability of light sources. Thephotoinitiators used should be able to absorb at the wavelength(s) ofthe light source used. Because the process of the present invention doesnot require thermal polymerization, the emulsions, and resulting foams,need not contain any thermal initiator or thermal initiator residue.

After the foam has been polymerized, the immiscible phase fluid willtypically still be present in the foam. This residual immiscible fluidmay be removed by drying the foam structure. Suitable drying methodsinclude, e.g., vacuum drying, freeze drying, squeeze drying, microwavedrying, drying in a thermal oven, drying with infrared lights, or acombination of these techniques.

The emulsions are typically prepared under low shear conditions, i.e.,methods providing gentle mixing of the continuous and dispersed phases,such as shaking, using an impeller mixer or pin mixer, and using amagnetic stir bar. High shear conditions may be achieved with, a rotorstator mixer, a homogenizer, or a microfluidizer. Properties of foams ofthe present invention such as cell sizes, cell size distributions, andnumber of windows may be influenced by the agitation methods oragitation speeds used to make the emulsions. Cell sizes will also dependon factors such as the type of monomer(s) and surfactant(s) used, andthe volume ratio of immiscible phase to reactive phase.

Emulsions of the present invention may be made by continuous or batchprocesses. Suitable apparatus for making the emulsions continuouslyinclude static mixers, rotor stator mixers, and pin mixers. Greateragitation may be achieved by increasing the speed of agitation or usingapparatus designed to disperse the emulsifier more finely in theemulsion during the mixing process. Batch process emulsions may be madeby mixing or shaking the combined ingredients, by hand or by machine.Greater agitation in a batch process may be achieved, by using e.g., adriven impeller mixer or a three-propeller mixing blade.

The foam microstructure can also be influenced by the amount of timeelapsed between preparation of the emulsion and polymerization.Typically, as more time elapses, the emulsion begins to break down,i.e., cells coalesce and/or cell walls collapse. A foam made from anaged emulsion may have larger and fewer cells than a foam made from thesame emulsion but polymerized soon after the emulsion is made. Aging theemulsion can also affect the size, number, and location of theinterconnecting windows, which can alter the fluid uptake behavior ofthe resulting foam.

Adding a salt to the immiscible phase can change the cell windowstructures because it forces the lipophilic monomer out of theimmiscible phase and into the reactive (oil) phase thereby improvingemulsion stability. i.e., the emulsion resists breaking down intodistinct layers of reactive and immiscible phases. Salts are not neededin the present invention, but may be used.

As mentioned above, a variety of mixing techniques can be used to makethe emulsions of the present invention. For a givenreactive-to-immiscible phase ratio, each of these mixing techniques hasthe potential to produce a slightly different emulsion microstructure.High shear and low shear mixing conditions can both be used. If thecomponents of the reactive or immiscible phases have high viscosities,low shear conditions may not produce a foam. High shear conditions mayproduce foams having relatively higher densities because using highshear conditions usually results in less incorporation of the immisciblephase into the reactive phase as compared to using low shear. The extentof the microstructure variability is evident in the following figures(FIG. 9 shows a foam made with a continuous rotor-stator mixer, FIG. 7(Example 27) shows a foam made with a static mixer, and FIG. 10 shows afoam made with a pin mixer). The desired microstructure will depend onthe specific foam application of interest. The various microstructureswill provide different properties in terms of pressure drop, fluid flow,tortuosity of the fluid path, surface area, etc. The ability to makemany different microstructures with the same starting materials makesthis process of the current invention a particularly versatile one.

Many polymeric foams of the present invention made from HIPEs aretypically relatively open-celled. This means that most or all of thecells are in unobstructed communication with adjoining cells althoughclosed cell foams may also be made. The cells in such substantiallyopen-celled foam structures have intercellular windows that aretypically large enough to permit fluid transfer from one cell to anotherwithin the foam structure.

The substantially open-celled foam structures will generally have areticulated character with the individual cells being defined by aplurality of mutually connected, three-dimensionally branched webs. Thestrands of polymeric material making up these branched webs can bereferred to as struts. The struts typically form a dimensionallylong-range macroscopic structure, in contrast to a loosely associatednetwork of particles.

Closed cell foams may also be made by the process of the presentinvention. Whether foam cells are open or closed will largely depend onthe amount of surfactant in the emulsion. This phenomenon, and theappropriate surfactant content needed to obtain a closed-cell foam, aredescribed, for example, in Williams, J. M. and Wrobleski, D. A., SpatialDistribution of the Phases in Water-in-Oil Emulsions. Open and ClosedMicrocellular Foams from Cross-Linked Polystyrene, Langmuir Vol. 4, No.3, 1988, 656-662.

The HIPE foams of the present invention preferably have densities ofgreater than 0.005 g/cc more preferably greater than 0.01 g/cc, andtypically have densities of less than 0.25 g/cc. Foam cells, andespecially cells formed by polymerizing a monomer-containing reactivephase that surrounds a relatively monomer-free immiscible phase droplet,tend to be substantially spherical in shape. Cell sizes typically rangefrom 1 to 200 micrometers and are preferably less than 100, morepreferably less than 50, most preferably less than 20 micrometers, formost applications. The HIPE foams typically have 4 to 100 intercellularwindows, preferably 2 or more, more preferably 8 or more. The windowspreferably having diameters of 0.1 to 25 μm, preferably 0.1 to 10 μm.The non-HIPE foams of the present invention typically have aninterconnected channel structure. They preferably have densities ofgreater than 0.20 g/cc, and typically have densities of 0.25 to 0.98g/cc.

The foam densities listed here assume oil phase components having adensity of approximately 1 g/cc. If denser materials are used in thereactive phase the foam density can be greater than those listed asranges herein.

Foam materials of the present invention having two major parallelsurfaces may be from 0.05 to 10 millimeters thick, preferably 8 mm orless. The emulsions should not be made into a shape or thickness thatprevents radiation from penetrating at least halfway through it (so theemulsion can be fully polymerized by exposing each side). The allowablethickness will depend on the materials used, the nature of thepolymerizing actinic radiation, the photoinitiator type, and the amountof photoinitiator used. Decreasing the amount of photoinitiator candecrease the light absorption of the emulsion and may increase lightpenetration, depending on the light scattering effects of the emulsion.If scattering effects dominate, reducing the photoinitiator level willhave little effect on light penetration. Foams thicker than 8-10 mmcould be made by photopolymerizing a sequence of layers, with each newemulsion layer being placed on the previously polymerized layers andbeing of a thickness that would allow light to penetrate through itsentire depth.

Articles

The foams may be made into sheets, slabs, and other shapes. Thethickness of a an article can vary and may depend on process conditionssuch as the composition, wavelength and intensity of the curing light,and photoinitiator type and amount.

Layered articles may be made by layering the emulsion with otherpolymerizable or non-polymerizable materials so long as the materialsused are sufficiently transparent to the wavelength absorbed by thephotoinitiator in the emulsion, or so long as the foam comprises anouter layer of a structure such that the emulsion can be fullypenetrated by a sufficient amount of the radiation at the wavelengthbeing used. Multilayer articles may also be made by post-productionprocesses such as laminating. The layered articles may have a myriad ofdifferent properties depending on the composition, bulk density, cellsizes, window sizes, etc. of the foams. The layers may differ by morethan 20% with respect to, for example, content of a particular componentand density.

Multi-regional articles may be made by a number of methods. They may bemade by adding pieces of polymerized foam to an emulsion that issubsequently cured. They may also be made by carefully mixing two ormore emulsions prior to curing. The different regions or areas in theresulting foam article may differ with respect to composition, density,color, or other properties.

The foams of the present invention are suitable for many uses including,for example, membranes, absorption (such as when used as a wounddressing), filtering, sound dampening, and insulation. By varying thestarting material and processing conditions, the foam structure can betailored to have particular properties suitable for their intended uses.

Some foams of the present invention will remain in a collapsed stateafter removal of the immiscible fluid. The inventors found that as thesefoams absorb fluid and change from a collapsed state to a rehydratedstate, their bulk densities decreased by at least 10%. These foams canbe transparent or translucent when dry and can become opaque as theyabsorb fluid. When the foams absorb organic liquids, it is possible forthem to swell beyond their original dimensions.

Foams comprised of pressure sensitive adhesives can provide adhesivefoam articles that do not require the separate application of anadhesive layer. This is beneficial in some applications requiringadherence of the foam to another surface.

When used for fluid absorption, most preferred polymeric foams aresufficiently hydrophilic to permit the foam to absorb aqueous fluids.The level of hydrophilicity can depend on the starting material. Foamscreated from an emulsion having a non-water immiscible phase andmonomers that are water soluble would be very hydrophilic and can takeup water better than foams made with water insoluble monomers.Hydrophilicity may also be modified by post-production processes knownin the art.

The foams of the present invention are generally hydrophilic and mayprovide desirable fluid handling properties such as good wicking andfluid distribution characteristics. These characteristics help verticalwicking, i.e., fluid wicking in a direction primarily normal to a majorsurface of the foam article. This is a desirable performance attributefor many absorbent foams because any imbibed fluid may be quickly movedaway from the impingement zone. Foam articles that provide verticalwicking allow absorbed fluid to be moved from the foam surface to deeperwithin the absorbent core of the article. These characteristics helptransport imbibed fluid away from the initial impingement zone and intothe unused balance of the foam structure, which allows subsequent fluidflows to the initial impingement zone to be accomodated. The HIPE foamsof the invention can absorb at least two and one-half times their weightin fluid, preferably up to, and greater than, 15 times their weight. Thenon-HIPE foams typically absorb 1 to 3 times their weight in fluid.

The foams can also have a relatively high storage capacity as well as arelatively high fluid capacity under load, i.e., under compressive load.The foams may be made to be sufficiently flexible and soft to besuitable for use against skin.

The fluid handling properties of a foam can be related to the foam'scapillary structure. Foams having larger cell and window sizes tend toacquire fluid quickly but do not distribute fluid sufficiently againstthe force of gravity, nor do they store fluid effectively. Conversely,foams having smaller cell and window sizes are able to wick fluidagainst the force of gravity and store the fluid tightly, but aretypically slower to acquire fluid.

Foams of the invention having different absorption characteristics maybe layered to produce an absorbent article having layers of foams suitedfor fluid acquisition and distribution alternating with layers of foamsthat are suited for fluid storage.

In addition, patterned foam articles can be produced by shaping andcuring the emulsion while in contact with a microstructured surface.After curing, the foam is separated from the microstructured surface andthe foam retains the geometrical pattern of the surface. Theseconventional techniques are described in U.S. Pat. No. 5,691,846,incorporated by reference. The microstructured surface can be chosenfrom a wide variety of geometrical shapes that include cavities,channels, posts, or profiles. The pattern can be selected depending onthe desired use of the foam.

Some foams of the present invention may be suitable for use as filters.The open-celled foams of the present invention can allow fluids(including air and liquids) to pass through, while the cells and windowscan trap particles. The optimum foam structure, including cell sizes andnumber of windows, will depend on the fluid being filtered and the sizeof the particles to be removed.

Emulsion

Reactive Phase

The continuous (reactive) phase of an emulsion of the present inventioncomprises monomers that form the polymer matrix, or struts, of the foamstructure after polymerization. The reactive phase comprises at leastone polymerizable material at least one emulsifier, and at least onemultifunctional crosslinking agent. However, the polymerizable materialand crosslinking agent may be the same multifunctional material.Additionally, the polymerizable material and the emulsifier may be thesame material, as in the case where the emulsifier is a reactivesurfactant. A reactive surfactant may make a foam more hydrophilic orhydrophobic, depending on its structure. A photo-initiator may also bepresent in the reactive phase.

Selection of particular types and amounts of monomers and optionalcomonomers, emulsifiers, and multifunctional crosslinking agents can beimportant in obtaining a foam having the desired combination ofstructural, mechanical, and fluid handling properties to render the foammaterials suitable for their intended uses. The components of thereactive phase should be substantially insoluble in the immisciblephase. Additives, including materials that do not participate in thepolymerization reaction, can also be included in the reactive phase.

Polymerizable Material

The polymerizable material component comprises one or more monomers thatmay be photopolymerized. If the immiscible phase is water, thepolymerizable material should be an ethylenically-or-acetylenicallyunsaturated substantially water-insoluble monomer. If the immisciblephase is nonaqueous, the polymerizable material may be acationically-curable monomer, an ethylenically- oracetylenically-unsaturated monomer, or a water-soluble monomer. Suitableethylenically or acetylenically unsaturated monomers include, forexample, the (C₁-C₁₄) alkyl acrylates such as acrylic acid, butylacrylate, n-butyl acrylate, hexyl acrylate, octyl acrylate, isooctylacrylate, 2-ethylhexyl acrylate, nonyl acrylate, isononyl acrylate,decyl acrylate, dodecyl (lauryl) acrylate, isodecyl acrylate, tetradecylacrylate; aryl and alkaryl acrylates such as benzyl acrylate andnonylphenyl acrylate, the (C₄-C₁₆) alkyl methacrylates such asmethacrylic acid, hexyl methacrylate, octyl methacrylate, nonylmethacrylate, isononyl methacrylate, decyl methacrylate, isodecylmethacrylate, dodecyl (lauryl) methacrylate, tetradecyl methacrylate;acrylamides such as N-octadecyl acrylamide, and substituted acrylamides.Other ethylenically-unsaturated monomers that will copolymerize withacrylates may also be used. Suitable types of co-monomers includemaleimides and azlactones. Styrenes are not preferred for the presentinvention due to their slow polymerization rate, but may be present inamounts of up to 4 weight percent when UV or visible light is used asthe radiation source. Suitable styrenes include (C₄-C₁₂) alkyl styrenessuch as p-n-octylstyrene. Combinations of any of these monomers may alsobe used.

Other functionalized acrylate monomers can also be used includingpolyester acrylates, urethane acrylates, and acrylates of epoxidizedoils.

If the immiscible phase is non-aqueous, monomers that are difficult topolymerize in the presence of water, e.g., cationically-curable monomersand water-soluble or highly hydrophilic monomers, may be used in thereactive phase. Suitable cationically-curable monomers include thosecontaining epoxide or vinyl ether functional groups. Suitablewater-soluble or hydrophilic monomers include poly(ethylene glycol)acrylates of various molecular weights. The monomers listed above foraqueous emulsions may also be used with an emulsion having a non-aqueousimmiscible phase.

Pressure Sensitive Adhesive (PSA) materials may also be used as aco-monomer. By proper selection of monomer(s), surfactant(s),initiator(s), and crosslinker(s), as known in the art foams with PSAproperties can be produced.

The reactive phase may also comprise multifunctional monomers and/oroligomers. These multifunctional materials may operate as both thepolymerizable material and crosslinking agent because the crosslinkingfunctionality can be introduced into the reactive phase via acrosslinking site on a monomer or a separate crosslinking species. Insuch a case no other ethylenically-or acetylenically-unsaturated monomeris necessary in the reactive phase.

The polymerizable material component may comprise between 50 and 99,preferably 80 to 95, weight percent of the reactive phase.

Crosslinking Agents

Crosslinking agents are typically present to tie polymer chains togetherto create a more three-dimensional molecular structure. Selection of theparticular type and amount of crosslinking agent will depend on thestructural, mechanical, and fluid-handling properties desired in theresulting foam. Suitable crosslinking agents include monomers containingtwo or more ethylenically-or acetylenically-unsaturated groups such aspolyfunctional acrylates, methacrylates, acrylamides, methacrylamides,and mixtures thereof. These include di-, tri-, and tetra-acrylates; aswell as di-, tri-, and tetra-acrylamides; di-, tri-, andtetra-methacrylates; di-, tri-, and tetra-methacrylamides, and mixturesof these monomers. Specific examples include diethylene glycoldiacrylate, trimethylol propane triacrylate, ethoxylatedtrimethylolpropane triacrylate, urethane acrylates, epoxy acrylates,polyester acrylates, oligomeric diacrylates.

Suitable acrylate and methacrylate crosslinking agents can be derivedfrom diols, triols, and tetraols, that include 1,10-decanediol,1,8-octanediol, 1,6-hexanediol; 1,4-butanediol; 1,3-butanediol;1,4-but-2-enediol; ethylene glycol; diethylene glycol;trimethylolpropane; pentaerythritol; hydroquinone; catechol; resorcinol;triethylene glycol; polyethylene glycol; sorbitol; divinyl ethers anddiepoxides; and the like.

If the emulsion has a nonaqueous immiscible phase, crosslinking agentssensitive to water such as diepoxides and divinyl ethers can be used inthe reactive phase. Emulsions having non-aqueous immiscible phases canalso use the crosslinking agents used in aqueous emulsions.

Crosslinking agents may comprise from 1 to 99 weight %, preferably 2 to75 weight %, of the reactive phase.

Emulsifiers

Emulsifiers are also a component of the reactive phase of emulsions inthe present invention. Suitable emulsifiers include reactive surfactantsand non-reactive surfactants. Reactive surfactants, havingethylenically-or acetylenically-unsaturated bonds, can participate inthe polymerization and crosslinking of the the polymerizing materials inthe reactive phase and thereby become part of the foam structure.Reactive surfactants are typically preferred over non-reactivesurfactants because they do not leach out of the resulting foam articleduring use. This can be particularly beneficial in applications wherethe foam comes into contact with skin.

In a water-in-oil emulsion, the emulsifier preferably has a hydrophilicto lipophilic balance (HLB) of 3 to 14, usually 4 to 6, depending on themonomer(s) used.

Suitable classes of non-ionic emulsifiers for water-in-oil emulsionsinclude polyoxyethylenated alkylphenols, polyoxyethylenatedstraight-chain alcohols, polyoxyethylenated polyoxypropylene glycols,polyoxyethylenated mercaptans, long-chain carboxylic acid esters,alkanolamine condensates, tertiary acetylenic glycols,polyoxyethylenated silicones, N-alkylpyrrolidones, fluorocarbon liquids,and alkylpolyglycosides. Specific emulsifiers most suited towater-in-oil emulsions include sorbitan monoleate, glycerol monoleate,polyethylene glycol (200 molecular weight) dioleate, Castor oil,glycerol monoricinoleate, distearyl dimethylammonium chloride, dioleyldimethylammonium chloride, and bis-tridecyl sulphosuccinic acid (sodiumsalt). Cationic and anionic surfactants can also be used as emulsifiersin this invention. When the immiscible phase is non-aqueous, otherclasses of emulsifiers, such as fluorocarbon liquids, are available inaddition to those listed above. In cases of cationic polymerization, itis preferable to use a non-ionic surfactant to avoid interfering withthe polymerization reaction.

Suitable reactive surfactants for the water-in-oil emulsions includemethoxypoly(ethyleneoxy) ethyl acrylate having 1 to 40 oxyethylenegroups, alkylene polyalkoxy sulfate (MAZON SAM 211-80, BASF, MountOlive, N.J.), and copolymerizable alkoxy surfactant (MAZON SAM-185 nowknown as ABE 1215, BASF, Mount Olive, N.J.). The emulsifiers listed atcol. 20, lines 55 et seq, and col. 21-22 of U.S. Pat. No. 5,856,366 mayalso be used in the present invention.

These same emulsifiers and surfactants, as well as others, can be usedwhen the immiscible phase is nonaqueous.

The type of surfactant used can affect the microstructure of theresulting foam. The applicants found that depending on the reactivesurfactant used increased emulsion agitation resulted in different cellsizes and/or number of cell windows.

Emulsifiers typically comprise up to 30 weight percent of the reactivephase.

Photoinitiators

Photoinitiators can rapidly and efficiently respond to a light sourcewith the production of radicals and other species that are capable ofinitiating a polymerization reaction. Preferably the photoinitiatorsused in the present invention absorb at wavelengths of 200 to 800nanometers, more preferably 300 to 800 nanometers, most preferably 300to 450 nanometers. The photoinitiator provides a convenient trigger forthe polymerization reaction. If the photoinitiator is in the reactivephase, suitable types of oil-soluble photoinitiators include benzilketals, α hydroxyalkyl phenones, α amino alkyl phenones, acylphospineoxides. Specific initiators include 2,4,6-[trimethylbenzoyldiphosphine]oxide in combination with 2-hydroxy-2-methyl-1-phenylpropan-1-one (50:50blend of the two is sold by Ciba Geigy as DAROCUR 4265); benzil dimethylketal (sold by Ciba Geigy as IRGACURE 651); α, α dimethoxy-α-hydroxyacetophenone (sold by Ciba Geigy as DAROCUR 1173); 2-methyl-1-[4-(methylthio) phenyl]-2-morpholino-propan-1-one (sold by Ciba Geigy as IRGACURE907); Oligo [2-hydroxy-2-methyl-1-[4-(1-methylvinyl) phenyl] propanone](sold as ESACURE KIP EM by Lamberti s p a);Bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (sold by Ciba Geigy asIRGACURE 819). Other suitable initiators are those disclosed in U.S.Pat. No. 5,545,676, PCT/US98/04458, and PCT/US98/04029, all of which areincorporated by reference.

Photoinitiators may comprise between 0.05 and 10.0, preferably between0.2 and 10, weight percent of the reactive phase. Lower amounts ofphotoinitiator allow light to better penetrate the emulsion, which canprovide for polymerization deeper in the foam layer. However, there mustbe enough initiator to initiate the polymerization and overcome oxygeninhibition. Further, light scattering by the emulsion, which alsoaffects light penetration depth, is not affected by photoinitiatorconcentration.

Reactive Phase Additives

The reactive phase may contain inert ingredients, such as polymers thatare dissolved, but do not undergo polymerization. These ingredients mayadd strength or toughness to the polymerized foam. Suitable monomeradditives include isoprene, butadiene, 1,3-pentadiene, 1,3,7-octatriene,and β-myrcene. Suitable polymer additives include polyisoprene,polyethylene, polypropylene, polybutadiene, and acrylic tougheners.Other suitable reactive phase additives include flame retardants,fillers, CaCO₃, and carbon black.

The reactive phase may also comprise materials that can incorporatesubsequently reactive functional groups into the foams during theirfabrication. Many functional groups can be incorporated as vinyl groups(e.g., vinyl dimethyl azlactone) or acrylate esters or other acrylateand methacrylate groups (e.g., hydroxyethyl acrylate, acrylamide,butylmethacrylates). Reactive functional groups that may be incorporatedinclude carboxylates, amines (including primary, secondary, tertiary,and quarternary amines and polyamines), sulfhydryls, azlactones,aldehydes, epoxides, maleimide isothiocyanates, isocyanates, n-alkylgroups (e.g., butyl, octyl, and octadecyl groups), phenyl and benzylgroups, cycloalkyl groups, hydroxy and hydroxyethyl groups, amidesincluding (acrylamides), sulfonates, sulfonamides, phosphates,polyphosphates, iminodiacetates, various bypryridyl groups, salicylates,polyethers (including crown and cryptand ethers), and cyclodextrans.

When the reactive phase contains additives, the polymerizablematerial(s) may comprise less than 50% of the reactive phase.

Immiscible Phase

The immiscible phase may comprise any suitable fluid that issubstantially immiscible with the polymerizable material(s) in thereactive phase and is a liquid at operating conditions. The mostfamiliar immiscible phase is water. The immiscible phase may comprise aphotoinitiator or emulsifier. Unlike most thermally-cured emulsions, theemulsions of the present invention do not require salts to stabilize theemulsion, although they may be added.

The immiscible phase fluid should have a viscosity of at least 1centipoise at the use temperature. The upper viscosity limit for theimmiscible phase will depend on the viscosity of the reactive phase andthe desired foam structure. The immiscible fluid should not absorb lightin the same wavelength as the photoinitiator being used. Suitable fluidsother than water include, for example, fluorocarbon liquids and organicliquids in which the reactive phase is immiscible. Using a non-aqueousdiscontinuous or cocontinuous phase can allow different types ofreaction chemistries for polymerizing the foams. For example, cationicphotopolymerization or free radical polymerization of water soluble andvery hydrophilic materials.

Photoinitiators

Photoinitiators soluble in the immiscible phase may be used in thepresent invention. Suitable photoinitiators include those disclosed inU.S. Pat. No. 5,545,676, incorporated by reference. The photoinitiatorused should absorb light at the wavelength used to polymerize theemulsion, and should be effective for the type of polymerization used,e.g., free radical or cationic. Preferably the photoinitiators used inthe present invention absorb at wavelengths of 200 to 800 nanometers,more preferably 300 to 800 nanometers, most preferably 300 to 450nanometers.

Salts

Salts in the immiscible phase can increase the stability of the emulsionby minimizing the tendency of monomers, comonomers, and crosslinkersthat are primarily soluble in the reactive phase to partition into theimmiscible phase. Suitable salts for an aqueous immiscible phase includemono-, di-, or tri-valent inorganic salts including water-solublehalides, e.g., chlorides, nitrates, and sulfates of alkali metals andalkaline earth metals such as sodium chloride, calcium chloride, sodiumsulfate, and magnesium sulfate and other salts described in U.S. Pat.No. 5,352,711, incorporated by reference. Hydratable inorganic salts mayalso be incorporated into the foams to increase hydrophilicity. Aqueoussalt solutions may be used to treat the foams after removal of, or aspart of the process of removing, a residual aqueous immiscible phasefrom a just-polymerized foam.

When the immiscible phase is non-aqueous, salts having organic cationsor anions may be used. Suitable salts include, for example, borates,trifluoromethane sulfonates (triflates), and hexafluorophosphates.

If present in an emulsion of the present invention, the salts preferablycomprise less than 0.2 wt %, more preferably less than 0.1 wt % of theimmiscible phase.

Immiscible Phase Additives

The immiscible phase may contain additives such as ion exchange beads,fibers, and particulates. If the immiscible phase is removed afterpolymerization, these additives may remain in the foam by coating ontothe interior surfaces of the foam cells or structure through physicalentrainment or through deposition during immiscible phase removal. Forexample, evaporation can leave salts behind. Soluble species, such aspolymers, might also be added to the immiscible phase to provideenhanced mechanical strength to the emulsion or the polymerized foams.

Emulsion Additives

The emulsion may also include additives that are not soluble in eitherthe reactive or immiscible phase. Examples of suitable additives includeion exchange beads, fibers, particles, other foams, as described in U.S.Pat. No. 5,037,859, incorporated by reference, pigments, dyes, carbonblack, reinforcing agents, solid fillers, hydrophobic or hydrophilicsilica, calcium carbonate, toughening agents, flame retardants,antioxidants, finely ground polymeric particles (e.g., polyester, nylon,polypropylene, or polyethylene), expandable microspheres, glass beads,stabilizers (e.g., UV stabilizers), and combinations thereof.

The additives may be added in amounts sufficient to obtain the desiredproperties for the foam being produced. The desired properties arelargely dictated by the intended application of the foam or foamarticle. The additives should be selected such that interference withphotopolymerization is minimized.

This invention may be illustrated by way of the following examples.

EXAMPLES Test Methods

Foam Density

The weight of individual dry foam samples was measured on a MettlerToledo balance (Model AG 245, Greifensee, Switzerland) and anArchimedes-type device was employed to measure water displacement.Initially, the density measurements were complicated by the fact thatthe samples absorbed water very rapidly. To remedy this problem, thesamples were spray coated with clear acrylic lacquer and allowed to dryprior to water displacement measurement. The lacquer created a coatingand sealed the pores so water absorption during density measurement wasgreatly reduced.

The density of some samples was determined by an alternate method basedon the amount of water uptake of the sample with the assumption that allthe voids in the foam become filled by water, and that the struts of thefoam are not swollen by water.

Absorbency

Initial sample weight measurements were taken on all dry foam pieces.The samples were then submerged for a predetermined amount of time indeionized water at room temperature. The samples were removed from thewater and weighed. The final absorbency ratio was reported as the ratioof wet sample mass (grams) to initial dry sample mass (grams) after thesample had reached its maximum capacity for water uptake. The finalcapacity was typically reached within 30 seconds.

Gurley Number

The Gurley number of a sample represents the amount of time it takes toforce a certain volume of air through a fixed area of a sample with aconstant pressure. It is a measurement of the permeability of thesamples to gases. Samples of the present invention were tested on aTeledyne Gurley Tester (Model 4110, Troy, N.Y.) with a GENUINEGURLEY4320 automatic digital timer. The porous foam samples were placedbetween clamp plates and pressure was applied to a cylinder pistonpositioned on the upstream side of the sample. All samples had 50 ml ofair forced through an area of (1 in²). Gurley measurements were done insets of four on samples without removing and replacing the sample in theapparatus. The number reported is the average of the four valuesobtained.

Tensile Test

Tensile testing was conducted by using a freshly sharpened die to cutsamples into a shape having a rectangular center portion for testing andwider ends for fastening the sample into pull arms. The center sectionhad a width of 0.5 cm and a gage length of 1.5 cm. Three to fivespecimens were used for each test. Sample thickness was measured with adigital micrometer for each sample before the test. A Sintech 20 TensileTester with Test Works software (available from MTS Systems Corp, EdenPrairie, Minn.) was used to acquire data.

A 150-gram load cell was used (calibrated electronically), with a20-gram weight. The samples were pulled in the length-wise direction at2.54 cm/min. Soft adjustable spring rate fixtures were used to grip thespecimens between the crossheads during the test.

Scanning Electron Microscope

The SEM micrographs were taken with either a JEOL 35C or a JEOL Model840 SEM (Peabody, Mass.). Foam samples that did not exhibit any collapseupon drying (removal of the immiscible phase) were freeze fracturedunder liquid nitrogen, sputter coated with either gold or a goldpalladium (60/40) mixture, and the cross-sections were imaged. Foamsthat collapsed partially or completely upon drying were imaged in theswollen state by performing a crude freeze-drying procedure. The freezedried samples were prepared by swelling them completely in water (15-30minutes), then immersing them in a pool of liquid nitrogen to freezethem in the swollen state. The pool of liquid nitrogen (containing thefrozen sample) was placed into a vacuum evaporator (Denton Vacuum ModelDV-502A, Moorestown, N.J.) and the sample was left under vacuum forapproximately 16 hours. When the sample was removed from the evaporator,it was dry but was not in the collapsed state. The dry sample crosssection was then sputter coated and imaged as described above.

Example 1

Example 1 describes a batch process for making the foam emulsions of thepresent invention. The oil phase consisted of twelve grams of isobornylacrylate (SR 506, Sartomer Co., Exton, Pa.), 69 grams of 2-ethyl hexylacrylate (Aldrich Chemical Co., Milwaukee, Wis.), 15.1 grams of sorbitanmonooleate (Aldrich Chemical Co., Milwaukee, Wis.), 12 grams oftrimethylolpropane triacrylate (TMPTA-N, UCB Chemicals, Smyrna, Ga.),and 7.8 grams of DAROCUR 4265 (Ciba Geigy, Hawthorne, N.Y.), which wereadded to a glass jar and mixed by hand. This mixture comprised the oilphase mixture. 51.69 grams of this oil phase mixture were placed into aplastic tri-pour beaker. The mixture was agitated continuously with aJiffy Stirrer (an air-driven impeller containing a Jiffy Stir mixingattachment, Cole Parmer item number P-04541-00, Vernon Hills, Ill.). Therotational speed of the Jiffy Stirrer was affected by the viscosity ofthe medium being stirred, so the rotational rate of the Jiffy Stirrerwas neither known nor exactly controlled. The diameter of the Jiffy StirImpeller was 6.67 cm.

Deionized water was added slowly (approximately 2 ml every 6 seconds) tothe agitating oil phase mixture, and the total weight of the mixture wasmeasured periodically on a balance. As the water content of the emulsionincreased, so did the viscosity. After 574.31 grams of water had beenadded, the emulsion had a uniform consistency with a small amount offree water at the top. A sample was withdrawn from the center of theemulsion. The sample was allowed to sit in a glass beaker for 15 minutesprior to being polymerized, during which time a small amount of waterseparated from the sample. The sample had a water:oil ratio ofapproximately 11:1.

The polymerization was completed by pouring the liquid emulsion onto apiece of quartz that had TEFLON spacers forming a dike. A second pieceof quartz was placed on top of the dike creating an enclosed sheet ofemulsion 0.20 cm thick. The encased sample was then passed under aFusion (Gaithersburg, Md.) F600 Irradiator equipped with a D Bulboperating at 100% power, in focus, with a conveyer speed of 20 feet/min.The sample received a total of 6 passes under the Fusion light (3 oneach side) with alternating sides exposed to the light on each pass.Quantitative light measurements for a single pass under the F600 D lamphave been included in Table 1. The measurements were taken with a PowerPuck (10 Watt, EIT, Sterling, Va.). After exposure to the light, thesample was a wet solid, so it was placed on a piece of silicone-coatedrelease liner and put into a forced-air oven (Despatch Model LAC1-38A-4,Minneapolis, Minn.) at 70° C. overnight to dry. Micrographs of thissample are shown in FIG. 1.

The density of the dry foam sample was 0.20 grams/cc as measured bywater displacement. The sample was coated with a thin layer of a clearacrylic spray paint before measurement (to prevent the sample fromswelling when immersed in water). A second density measurement, based onthe water uptake of the sample indicated that the density of the foamdecreased to 0.08 grams/cc when wet.

TABLE 1 Light measurements made with a 10 Watt Power Puck Spectral RangeJoules/cm² Watts/cm² UVA 2.213 4.464 UVB 0.613 1.146 UVC 0.034 0.056 UVV1.269 2.647

Examples 2 and 3

Examples 2 and 3 were made using a reactive surfactant (emulsifier) inthe emulsion and different mixing methods.

Examples 2 and 3 were made by mixing isobornyl acrylate (0.4020 grams),2-ethyl hexyl acrylate (2.2984 grams), SAM 211-80 (0.4995 grams, BASF,Mount Olive, N.J.), trimethylolpropane triacrylate (0.4067 grams), andDAROCUR 4265 (0.2448 grams), in a glass beaker by hand to create an oilphase mixture.

The oil phase mixture was agitated during emulsion preparation with amagnetic stir plate (Catalog Number 58935-351, VWR Scientific, Chicago,Ill.). Deionized water (25.90 grams) was added dropwise (approx. 1 dropper second) to the oil phase during agitation via a separatory funnelmounted over the stir plate. A homogeneous, opaque emulsion was preparedby this method. Example 2 comprises one half of the emulsion removedafter the water addition was complete. Example 2 was polymerizedimmediately, using the same method described in Example 1. Example 3comprises the other half of the emulsion. It received some additionalagitation using a three-blade air-driven impeller for less than oneminute. After the additional agitation, the Example 3 emulsion waspolymerized (also as described in Example 1). The polymerized sampleshad shiny white surfaces, and were placed on a silicone-coated releaseliner in a forced-air oven overnight at 70° C. to dry. The dried samplescollapsed completely, becoming translucent yellow disks that had somesplitting marks caused by drying. After soaking in water for 10-15minutes, the dried samples completely re-hydrated, became white andopaque again, and regained their original dimensions. The collapsedsamples were submitted for SEM analyses. Photomicrographs were obtainedof the collapsed structures as well as of the swollen structure (whichwas preserved after crudely freeze-drying the sample) of each of thesamples. The micrographs are included in FIG. 2.

Examples 4-9

Examples 4-9 were made from the same emulsion but each example wasallowed to age for a different length of time before polymerization.

Example 4 was made by adding to a 1-Liter plastic tri-pour beakerisobornyl acrylate (8.0097 grams), diethylene glycol diacrylate (9.4252grams SR230, Sartomer, Exton, Pa.), 2-ethylhexyl acrylate (42.0381grams), sorbitan monooleate (8.4300 grams), trimethylolpropanetriacrylate (4.5000 grams), DAROCUR 4265 (2.5061 grams), and MAZON SAM185 (1.62 grams, BASF) to create an oil phase mixture. The oil phasemixture was agitated with a Jiffy Stir Impeller (diameter of 6.67 cm(2.5 in.)) driven by an air motor. The agitation speed was not recorded.500 milliliters of deionized water was delivered at a rate ofapproximately 30 milliliters/min during the oil phase agitation. Example4, comprising a 20 g sample of the emulsion, was polymerized to athickness of 0.20 cm after the water addition was complete, followingthe procedure described in Example 1 at time zero (0). The remainingemulsion was allowed to reside at room temperature with a loose aluminumfoil cover over it. Examples 5-9 were 20 g samples withdrawn from theaging emulsion and polymerized at the following times, measured from thetime the emulsion was made: 15 minutes (Ex. 5), 59 minutes (Ex. 6), 164minutes (Ex. 7) 339 minutes (Ex. 8), and three days later (Ex.9). Theviscosity changed (decreased) the most between Examples 4 and 5. Theemulsion viscosity did not change appreciably (as observed visually) forthe remaining examples. The polymerized foam samples were dried in aforced-air oven overnight at 70° C. SEM micrographs were taken ofExamples 4, 5, and 9. The micrographs are included as FIG. 3.

The micrographs show that the emulsion structure is undergoing subtlechanges with time. This fact was also evidenced by the water uptakerates of the foams. Within 40 seconds of being immersed in water,Example 4 had absorbed approximately 6 times its weight in water, whileExample 5 had absorbed approximately 4.5 times its weight in water.Examples 8 and 9 absorbed less than one times their dry foam weightwithin 40 seconds. These different absorptions occurred even though thedensities of the foams were the same.

Examples 10-13

Examples 10-13 are foams of the present invention having differentdensities. Examples 10-12 were made from a single oil phase mixture. Theoil phase mixture was made by combining and mixing the followingcomponents: isobornyl acrylate (0.7972 grams), 2-ethylhexyl acrylate(9.2156 grams), sorbitan monooleate (2.0044 grams), trimethylolpropanetriacrylate (1.6568 grams), and DAROCUR 4265 (1.0764 grams). Thecomponents were stirred by hand and used as the oil phase for Examples10, 11 and 12. The density of the foam is determined by how much wateris added (dispersed) in the oil phase, with greater amounts of waterleading to lower density foams and possibly different microstructures.The oil phase mixtures were then agitated with a magnetic stir plateduring water addition via a separatory funnel (about 1 drop/sec).Deionized water in the quantity 50.24 grams was added to the Example 10oil phase, 12.45 grams of water were added to the Example 1 oil phase,and 25.05 grams of water were added to the Example 12 oil phase.

Example 13 was prepared from a different oil phase to produce a samplewith the same composition, but a different density than Examples 10-12.The oil phase mixture comprised isobornyl acrylate (0.4064 grams),2-ethylhexyl acrylate (2.3435 grams), sorbitan monooleate (0.5085grams), trimethylolpropane triacrylate (0.4160 grams), and DAROCUR 4265(0.2592 grams). Deionized water in the amount of 6.24 grams was added asdescribed above and an emulsion was created.

The emulsions were coated and polymerized into 0.20 cm thick sheets asdescribed in Example 1. After polymerization, the samples were placed ona silicone-coated release liner and dried in a forced-air oven for 48hours at 70° C.

The Gurley number, density and water uptake of the samples was measured.These data are included in Table 2. SEM micrographs were taken of theExamples. The micrographs are included as FIG. 4.

TABLE 2 Effect of Density on Gurley Number and Absorbency Ratio MeasuredDensity Gurley Number Absorbency Ratio Example (Grams/ml) (sec) (gramwet/gram dry) 10 0.08 2.3 12.5  12 0.16 7.4 6.5 11  0.29* 22.2 4.5 130.56 20.8 2.6 *The density of this sample was measured by displacement,but it was done without clear lacquer covering the sample. As a result,this is probably an overestimate of the true density.

Examples 14-16

Examples 14-16 have varying amounts of emulsifier (sorbitan monooleate.)

Example 14 was made by adding 0.3960 grams of isobornyl acrylate, 2.3120grams of 2-ethylhexyl acrylate, 0.4943 grams of sorbitan monooleate,0.4029 grams of trimethylolpropane triacrylate, and 0.2812 grams ofDAROCUR 4265 to a beaker. The oil phase was emulsified with 25.13 gramsof deionized water by continuous agitation on a magnetic stir plateduring dropwise water addition via a separatory funnel (at approximately1 drop/sec).

Example 15 was made by adding 0.4070 grams of isobornyl acrylate, 2.4033grams of 2-ethylhexyl acrylate, 0.4138 grams of sorbitan monooleate,0.4195 grams of trimethylolpropane triacrylate, and 0.2572 grams ofDAROCUR 4265 to a beaker. These oil phase components were well mixed.The oil phase of this sample was emulsified with 25.02 grams ofdeionized water in the same manner as described in Example 14.

Example 16 was made by adding 0.4009 grams of isobornyl acrylate, 2.4929grams of 2-ethylhexyl acrylate, 0.3132 grams of sorbitan monooleate,0.4062 grams of trimethylolpropane triacrylate, and 0.2594 grams ofDAROCUR 4265 to a beaker. These components were mixed well and arehereinafter referred to as the oil phase. The oil phase of this samplewas emulsified with 25.55 grams of deionized water in the same manner asdescribed in Example 14.

The emulsification formed white opaque emulsions for each example. Eachemulsion was poured between quartz plates (as described in Example 1),and polymerized into 0.20 cm thick sheets of foam. They were dried in aforced-air oven at 70° C overnight.

Example 16 did make an emulsion, but started to destabilize rapidly assoon as the agitation was stopped, presumably because there was not asufficient amount of emulsifier to adequately stabilize the emulsion.The rapidly-destabilizing sample was passed under the ultraviolet lightwithin 30 seconds after the emulsion was obtained. After drying, thecells of this foam appeared large even to the naked eye.

Scanning electron micrographs of the sample cross-sections have beenincluded in FIG. 5. The measured Gurley numbers, absorbency measurementsand measured densities have been included in Table 3.

TABLE 3 Emulsifier Concentration and Density, Absorbency Ratio, andGurley Number Gurley SMO Conc. Density Absorbency Ratio Number Example(wt % in oil phase) (g/ml) (gram/gram) (sec) 14 12.7 0.22 5.9 17.2 1510.6 0.18 4.2 14.7 16  8.1 0.18 5.1  5.7

Example 17

Example 17 was polymerized with a Xenon flashlamp.

Example 17 was made by mixing in a beaker isobornyl acrylate (0.4028grams), 2-ethylhexyl acrylate (2.3013 grams), sorbitan monooleate(0.5208 grams), trimethylolpropane triacrylate (0.4122 grams), andDAROCUR 4265 (0.2555 grams). These oil phase components were well mixed.The oil phase was emulsified with 25.52 grams of deionized water byadding the water dropwise at a rate of about one drop per second intothe oil phase during constant agitation with a magnetic stir plate. Aviscous white opaque emulsion resulted.

The emulsion was poured between two quartz plates (with 50 mil thickspacers) and passed under a Xenon flashlamp (Xenon Flashlamp, Model RC742, Woburn, Mass.). The flashlamp was operated with a pulse frequencyof 10 pulses per second with a peak intensity of 1800 Watts/cm². Thesample was sent through the light twice on each side (total of fourpasses) with alternating sides toward the light source at 30 feet/min.The sample was removed from the quartz, and placed on release liner in aforced-air oven to dry overnight at 70° C.

The process produced a crosslinked open-cell porous foam that partiallycollapsed upon drying. After drying, the sample had reduced considerablyin thickness and had many spotty transparent regions. When examined withthe SEM, the layering behavior in the dried sample was evident. When thesample re-hydrated, however, the layers of varying density were nolonger visible. The SEM photomicrographs of this sample are contained inFIG. 6.

Examples 18-26

A series of samples with different chemical compositions were preparedfor the purpose of investigating compositional effects on dry foamtensile strength.

Example 18 was prepared by combining in a beaker isobornyl acrylate(1.2032 grams), 2-ethylhexyl acrylate (1.4922 grams), sorbitanmonooleate (0.5288 grams), trimethylolpropane triacrylate (0.4034grams), and DAROCUR 4265 (0.2444 grams). These oil phase components werewell mixed by hand. The oil phase was emulsified with 25.93 grams ofwater by the dropwise addition of water via a separatory funnel duringconstant agitation with a magnetic stir plate. The emulsion was thenpolymerized between two pieces of quartz separated by 0.20 cm shims byexposure to a Fusion F600 D lamp in focus at 100% power, and 20 feet perminute with six passes (three each on alternating sides). Afterpolymerization, the sample was removed from the quartz plates and placedon a silicone-coated release liner to dry in a forced-air oven at 70° C.overnight.

Example 19 was prepared by combining in a beaker isobornyl acrylate(0.4400 grams), diethylene glycol diacrylate (1.2134 grams),2-ethylhexyl acrylate (2.4960 grams), sorbitan monooleate (0.5327grams), trimethylolpropane triacrylate (0.4034 grams), and DAROCUR 4265(0.2557 grams). These oil phase components were well mixed by hand. Theoil phase was emulsified with 24.95 grams of deionized water, asdescribed in Example 18, then it was polymerized as described in Example18. The resulting foam partially collapsed upon drying.

Example 20 was prepared by combining in a beaker an aromatic urethaneacrylate (0.9035 grams CN973J75, Sartomer Co., Exton, Pa.), isobornylacrylate (0.2060 grams), 2-ethylhexyl acrylate (1.6912 grams), sorbitanmonooleate (0.5094 grams), trimethylolpropane triacrylate (0.3938grams), and DAROCUR 4265 (0.2656 grams). These oil phase components werewell mixed. The oil phase was emulsified with 26.07 grams of deionizedwater while being agitated with a Jiffy Stir impeller (with diameter of1.25 inches) instead of the magnetic stir plate, due to its highviscosity. After being polymerized as described in Example 18, thissample was placed on a silicone-coated release liner in a forced-airoven at 70° C. to dry for approximately 48 hours.

Example 21 was prepared by combining in a beaker isobornyl acrylate(0.3979 grams), ditrimethylolpropane triacrylate (0.4800 grams SR355,Sartomer Co.), 2-ethylhexyl acrylate (2.2330 grams), sorbitan monooleate(0.5336 grams), and DAROCUR 4265 (0.2570 grams). These oil phasecomponents were well mixed. The oil phase was emulsified with 25.21grams of deionized water as described in Example 18. Afterpolymerization, this sample was placed on a silicone-coated releaseliner in a forced-air at 70° C. to dry for about 48 hours.

Example 22 was prepared by combining in a beaker isobornyl acrylate(0.4008 grams), aromatic urethane acrylate (0.5013 grams CN972, SartomerCo.), 2-ethylhexyl acrylate (1.4922 grams), sorbitan monooleate (0.5111grams), trimethylolpropane triacrylate (0.4038 grams), Bisphenol Aacrylate (0.4270 grams SR349, Sartomer Co.), and DAROCUR 4265 (0.25340grams). These components were well mixed and are hereinafter referred toas the oil phase. The oil phase was emulsified with 25.10 grams ofdeionized water as described in Example 18, and polymerized as describedin Example 18. After polymerization, this sample was placed on asilicone-coated release liner in a forced-air oven for approximately 48hours.

Example 23 was prepared by the addition of the following components to abeaker, isobornyl acrylate (0.4063 grams), 2-ethylhexyl acrylate (2.4257grams), sorbitan monooleate (0.5002 grams), trimethylolpropanetriacrylate (0.3930 grams), and DAROCUR 4265 (0.3112 grams). These oilphase components were well mixed. The oil phase was emulsified with25.00 grams of deionized water as described in Example 18, thenpolymerized and dried as described in Example 18.

Example 24 was prepared by combining in a beaker isobornyl acrylate(0.3933 grams), 2-ethylhexyl acrylate (0.8043 grams),tertbutylcyclohexyl acrylate (1.5033 grams TBCH, BASF), sorbitanmonooleate (0.5367 grams), trimethylolpropane triacrylate (0.4274grams), and DAROCUR 4265 (0.2526 grams). These oil phase components werewell mixed. The oil phase was emulsified with 25.92 grams of deionizedwater as described in Example 18. This sample was polymerized with aFusion F600 H lamp at 100% power, in focus at 20 feet/min with sixpasses total (alternating three per side). After polymerization, thissample was placed on a silicone-coated release liner and remained in aforced-air oven at 70° C. for approximately 48 hours. The thickness ofthis sample decreased upon removal of the immiscible phase.

Example 25 was prepared by combining in a beaker, isobornyl acrylate(0.4102 grams), polyester acrylate oligomer (0.8014 grams EBECRYL 1657,UCB Chemical Co.), 2-ethylhexyl acrylate (1.4999 grams), sorbitanmonooleate (0.5285 grams), trimethylolpropane triacrylate (0.3989grams), and DAROCUR 4265 (0.2481 grams). These components were wellmixed and are hereinafter referred to as the oil phase. The oil phasewas emulsified with 25.69 grams of deionized water. Half theemulsification was done using the magnetic stir plate, but when thesample became too viscous to agitate with the stir bar, the Jiffy Stirwas used to finish the emulsification. After polymerization, this samplewas placed on a silicone-coated release liner and remained in aforced-air oven at 70° C. overnight.

The samples were subjected to tensile testing. The results for peakstress, peak strain, energy and modulus are shown in Table 6. Peakstress and peak strain are the stress and strain values just prior tothe sample fracturing. Energy is calculated as the integral of thestress/strain curve. Elastic modulus is calculated as the slope of thestress/strain curve at 10% strain. Stress and Modulus are reported inkiloPascals. Energy is reported in Newton-meters.

TABLE 6 Tensile Test Results Peak Stress Peak Strain Energy ModulusExample (kPa) (%) (N · m) (kPa) 18 75 79.38 0.0568 172  19 110  111.07 0.0047 138  20 30 52.75 0.0156 97 21 31 48.71 0.0130 41 22 45 43.830.0161 48 23 34 57.10 0.0179 48 24 127  43.18 0.0616 1082  25 90 42.310.0382 193 

Example 26

Example 26 describes a continuous emulsion-making process for HIPEfoams. 37.06 grams of isobornyl acrylate, 233.06 grams of 2-ethylhexylacrylate, 48.16 grams of sorbitan monoleate, 40.15 grams oftrimethylolpropane triacrylate, 16.24 grams of DAROCUR 4265 were addedto a jar. These components, comprising the oil phase, were well mixed ona set of rolling mixers. The oil phase mixture was placed into apressure pot with 138 kPa (20 psi) of nitrogen pressure. The pressureforced the oil phase into a piece of plastic tubing where it was meteredusing a Zenith pump (Model QM, W. H. Nichols Company, Waltham, Mass.)and was fed into the static mixer train at a rate of approximately 13grams/min. A set of four static mixers (Statomix MC 06-32, ConProTecInc., Salem, N.H.) with the constricting portion removed were connectedin series. At the 3 junctions of the individual static mixers, water wasadded with pumps (Model RP G-150, FMI Fluid Metering, Inc., Oyster Bay,N.Y.). The FMI pump at the first addition point (closest to the monomeraddition) delivered approximately 57 grams/min, the second FMI pumpdelivered approximately 29 grams/min, and the third FMI pump deliveredapproximately 15 grams/min. A white emulsion exited the static mixertrain, and was polymerized (as described in Example 1). The foam wasdried overnight in a forced-air oven at 70° C. The density measured bythe water uptake method for this sample was 0.1 g/cc. SEM images of thecross-section of this foam sample are included in FIG. 7.

Example 27

Example 27 involves the production of a foam containing a urethaneacrylate, and displaying a unique interconnected cell structure unlikethat of the foams demonstrated in the other examples. The oil phase wascomprised of 22.83 grams of an aromatic polyester-based urethanediacrylate (CN 973 J75 monomer, Sartomer Co.), 4.00 grams of sorbitanmonooleate, 3.23 grams of trimethylolpropane triacrylate, and 0.99 gramsof DAROCUR 4265. These components were well mixed on the Jiffy Stirmixer in a plastic beaker prior to water addition. The emulsion was madeby adding deionized water at a rate of 20 grams/minute to the oil phaseduring continuous agitation with the Jiffy Stir mixer at an agitationrate of 520 rpm. After approximately 100 grams of water had been addedto the sample, the presence of one viscous white emulsion phase and oneseparate unemulsified water phase was evident. The agitation rate of themixer was increased to 830 rpm for several minutes in an attempt toincrease the water uptake into the emulsion. At the end of that time,the unemulsified water was decanted from the sample, and the emulsionwas polymerized as described in Example 1. The polymerized foam wasdried in a forced-air oven overnight at 70° C.

The foam density (measured by water uptake) was approximately 0.27 g/ml.Water absorption by this sample was quite rapid, reaching maximum uptakewithin 30 seconds. FIG. 8 contains SEM micrographs of the cross-sectionof the foams described in this Example.

Example 28

Example 28 describes a continuous emulsion-making process using acontinuous rotor-stator mixer (UTL-25 mixer, IKA Works, Inc.,Wilmington, N.C.). The following oil phase components were mixed onrollers in a closed jar: 43.2 g isobornyl acrylate, 251 g 2-ethylhexylacrylate, 55.3 g sorbitan monooleate, 43.2 g trimethylolpropanetriacrylate, and 27.1 g of DAROCUR 4265. This oil phase mixture wasmetered into the rotor-stator mixer at approximately 10 grams/min usinga Zenith Pump (Model QM, W. H. Nichols Company, Waltham, Mass.). Thenwater was fed to the rotor-stator mixer at a flowrate of approximately60 grams/min using a syringe pump. The mixer was operated at 13,500 rpm,and the mixing element used was an inline rotor-stator (Part S25KV-25-F-IL, IKA Works, Inc., Wilmington, N.C.). The emulsion exiting themixer was collected in a beaker then polymerized and dried as describedin Example 1.

The measured density (by the acrylic coating method) of the dry foamsample was 0.2 grams/cc. The dry foam absorbed 4.73 times its weight inwater after approximately 60 seconds of immersion. SEM micrographs ofthe foam cross-section are shown in FIG. 9.

Example 29

Example 29 describes a continuous emulsion-making process using a pinmixer. The mixing chamber of the pin mixer had an internal diameter ofapproximately 4 cm and a length of 18 cm. At 90 degree intervals aroundthe circumference of the mixing chamber were mounted pins which extendedinto the mixing chamber such that they came close to, but did not touchthe rotating mixing shaft. The mixing shaft had 10 elements, eachelement consisted of four appendages extending out at 90 degree angles.The elements were 6 mm wide and separated by approximately 1 cm on themixing shaft. The clearance between the mixing elements and the wall ofthe mixing chamber was approximately 0.5-1 mm. The rotation rate of thepin mixer was controlled by a motor and was monitored with a digitalreadout. The following oil phase components were measured into ajar andmixed by hand: 681.68 g of isobornyl acrylate, 1727.99 g of 2-ethylhexylacrylate, 426.68 g of sorbitan monooleate, 341.99 g oftrimethylolpropane triacrylate, and 111.55 g of DAROCUR 4265. The oilphase mixture was poured into a pressure pot (pressured to approximately2000 torr with nitrogen). A Zenith pump (described in Example 28),connected to the pressure pot, fed the oil phase mixture to the inlet ofthe pin mixer. At the same time a pump (Model QDX with a Q1 piston, FMIFluid Metering, Inc., Oyster Bay, N.Y.) fed deionized water from abucket into the pin mixer. At the time of collection of the emulsion ofExample 29, the monomer flow was approximately 13.8 grams/minute, andthe water flow was approximately 118 grams/minute. A valve at the outletof the pin mixer (which controlled flow and back pressure) was in thecompletely open position, and the pressure in the pin mixer was 1000 to5000 torr (20-30 psi) (as measured by a pressure guage on the pinmixer), while the pin mixer rate of agitation was 890 rpm. The emulsionwas collected from the outlet of the pin mixer and was polymerized anddried as described in Example 1.

The dry foam resulting from this process had a density (measured by thewater uptake method) of 0.10 grams/ml. The foam took up 8.6 times itsweight in water after approximately 60 seconds of immersion. SEMmicrographs of the dry foam cross-section are contained in FIG. 10. Thissample has a similar water to oil ratio as the sample made in Example26. A comparison of the foam microstructure from Example 26 and Example29 illustrates the impact of the emulsion-making method on the foammicrostructure, and ultimately, on the physical properties of the foam.

Other embodiments of the invention are within the scope of the followingclaims.

What is claimed is:
 1. A process for making a crosslinked polymeric foamcomprising: a) mixing a reactive phase comprising at least onepolymerizable material, at least one crosslinking agent, and at leastone emulsifier with at least one photoinitiator and a liquid immisciblewith the reactive phase to form an emulsion wherein the immiscibleliquid forms a discontinuous or co-continuous phase with the continuousreactive phase; b) shaping the emulsion; and c) exposing the emulsion toactinic radiation comprising ultraviolet or visible radiation of 200 to800 nanometers to form a crosslinked polymeric foam containing residualimmiscible fluid.
 2. The process of claim 1 further comprising removingat least a portion of the residual immiscible liquid from the foam. 3.The process of claim 1 further comprising exposing the crosslinked orcrosslinking foam to heat.
 4. The process of claim 1 wherein shaping theemulsion comprises forming the emulsion into a particular pattern orshape.
 5. The process of claim 1 wherein the polymerizable materialcomprises an ethylenically- or acetylenically-unsaturated monomer. 6.The process of claim 1 wherein the polymerizable material andcrosslinking agent are the same polyfunctional material.
 7. The processof claim 1 wherein the polymerizable material is a cationically-curablemonomer.
 8. The process of claim 1 wherein one polymerizable materialand the emulsifier are the same material.
 9. The process of claim 1wherein time is allowed to elapse between steps a) and c).
 10. Theprocess of claim 1 wherein the method of mixing the emulsion is selectedto produce a targeted microstructure structure in the resulting foam.11. The process of claim 10 wherein the mixing method comprises using apin mixer.
 12. The process of claim 1 wherein the immiscible liquid iswater.
 13. The process of claim 1 wherein the immiscible liquidcomprises at least 74 volume percent of the emulsion.
 14. The process ofclaim 1 wherein the photoinitiator is in the immiscible phase.
 15. Theprocess of claim 1 wherein the photoinitiator is in the reactive phase.16. The process of claim 1 wherein the reactive phase further comprisesmaterials that can incorporate functional groups into the foam.
 17. Theprocess of claim 1 wherein the emulsion is made continuously.
 18. Theprocess of claim 1 wherein an open cell foam is produced.
 19. Theprocess of claim 1 wherein a closed cell foam is produced.
 20. Theprocess of claim 12 wherein the water contains less than 0.1 weight %ionic salt.
 21. The process of claim 1 wherein the emulsion is one orboth of polymerized and crosslinked using ultraviolet or visibleradiation of 300 to 800 nanometers.
 22. The process of claim 1 whereinthe emulsion is crosslinked after less than 10 minutes exposure toactinic radiation.
 23. The process of claim 1 wherein the emulsion iscrosslinked after less than 10 seconds exposure to actinic radiation.24. The process of claim 1 wherein at least one ethylenicallyunsaturated material is an acrylate.
 25. The process of claim 1 whereinthe reactive phase further comprises non-polymerizable species.